Method and treatment of sludge having particles comprising metal, metal oxide or metal hydroxide intermixed therein

ABSTRACT

A method for treatment of sludge is disclosed, wherein the sludge has a liquid part and metal-containing particles intermixed therein. The particles comprise metal, metal oxide or metal hydroxide and the method comprises the following steps: atomising the sludge; supplying the atomised sludge to a flame of a burner provided in a furnace; bringing the liquid part of the sludge to vaporise by means of the flame while maintaining said flame by means of a separate fuel supply; and bringing at least part of the metal-containing particles to melt by means of the flame. This provides an efficient method for taking care of waste material from plants in the steel or petrochemical industry, for example.

FIELD OF INVENTION

[0001] The present invention relates generally to a method and anapparatus for treatment of sludge and more particularly a method and anapparatus for treatment of sludge having particles comprising metal,metal oxide or metal hydroxide-intermixed therein.

BACKGROUND

[0002] Sludge or slurry having waste materials intermixed therein posesa problem in today's industry. In the metallurgical industry, there isno suitable way of treating sludge from coke plants, blast furnaces,converters and rolling mills, for example oil-contamined scales andhydroxides from pickling. In most cases, these materials are depositedin some intermediate storage or taken to a landfill. Another area inwhich the problem of recovering materials is present is thepetrochemical industry, wherein a waste product in the form of sludge iscreated.

[0003] The pressure from both public authorities and customers to findnew solutions is constantly increasing. The earlier solution ofland-filling is no longer a feasible solution and is in many countriesillegal. Existing techniques for conversion and recovery are costly.

[0004] From an economic and environmental point of view, recovery isoften a preferred solution to the above-mentioned problem of taking careof the waste material. However, recovery often means some kind ofexternal processing, resulting in transportation to plants and processeslying beside the normal chain of processes.

[0005] A known solution to these problems is pelletization orbriquetting of the waste material for subsequent feeding to a furnace.However, this solution is accompanied with the problem of extra costsfor a separate plant for drying and subsequent pelletization of thewaste material.

[0006] The patent document DE 24 60 799 discloses a method of burningoil containing metal particles. The object of the disclosed method isthe destruction of the oil while avoiding unwanted exhaust particles.The burning relies solely on the energy supplied by the oil itself.

[0007] The patent document DE 42 41 283 discloses a process ofgasification wherein particles are recovered. No separate fuel supply isprovided.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to provide an improvedmethod and apparatus for treatment of sludge and more particularly amethod and an apparatus for treatment of sludge having particlescomprising metal, metal oxide or metal hydroxide intermixed thereinwherein the above-mentioned drawbacks with known techniques are avoidedor at least mitigated.

[0009] The invention is based on the realisation that the wet materialcan be fed directly to the flame of a burner wherein vaporisation iseffected and metal-containing particles are melted.

[0010] According to a first aspect of the present invention there isprovided a method for treatment of sludge as defined in claim 1.

[0011] According to a second aspect of the present invention there isprovided an apparatus for treatment of sludge as defined in claim 8.

[0012] With the method and the apparatus according to the invention, theproblems of prior art are overcome or at least mitigated. Instead ofrequiring a separate drying step, the wet material is treated directlyin a furnace, saving costs for extra equipment and also resulting in ashorter treatment time.

BRIEF DESCRIPTION OF DRAWINGS

[0013] The invention is now described, by way of example, with referenceto the accompanying drawings, in which:

[0014]FIG. 1 is a schematic diagram of a plant according to theinvention for treatment of sludge and other wet waste materials,

[0015]FIG. 2 is a sectional view of a burner used with the methodaccording to the invention, and

[0016]FIG. 3 is a schematic front view of the burner shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0017] In the following, a detailed description of the method and theapparatus according to the invention will be given. In the followingdescription the term sludge is used for the material supplied to theapparatus. However, it will be appreciated that this term includes othermaterials, such as slurry, slime, or mud comprising carbon containingparticles, including coke, char etc., and oil residue, waste from thecrude oil production, refineries, and petrochemical industries, sewagesludge etc. Also, in the preferred embodiment the metal content of thesludge is at least 5%, more preferably at least 20%, and most preferablyat least 50%.

[0018] Starting with FIG. 1, an overall diagram of a plant for treatmentof sludge and other wet waste materials, generally designated 10, isshown. The plant is built around a burner 20 installed in a side-wall ofa furnace 30. The burner is a so-called oxy-fuel burner and is thussupplied with fuel through a first feeding line 21 and with oxygenthrough a second feeding line 22. By oxygen is in this context meant agas with an O₂ content exceeding 21% and preferably so-called technicaloxygen having an O₂ content of approx. 90-100%.

[0019] Sludge is supplied to the burner through a third feeding line 23.The third feeding line 23 is connected to a feeder, generally designated40. The feeder 40 comprises a container 42, into which the wet startingmaterial in the form of sludge is fed. The sludge is directed from thecontainer 42 to an arrangement comprising a feeding pump 45 driven by amotor 46. By means of the feeding pump 45, the sludge is moved to theburner 20 at a rate determined by the speed of the feeding pump.

[0020] The burner 20 is also supplied with a suitable medium foratomising the sludge, such as oxygen or another gas etc. This atomisingmedium is supplied to the burner from a source (not shown) through theinput 25.

[0021] In the exemplary plant shown in FIG. 1, the furnace 30 is aseparate unit having an outlet 32 near the lower portion thereof for theoutput of molten metal containing particles recovered by the treatmentof the sludge. The furnace also comprises an exhaust outlet 34 in theupper portion thereof for the output of exhausts created from thevaporisation and combustion of the sludge during burning. In the bottomof the furnace there is gathered a charge 36 resulting from the materialsupplied to the furnace 30 through the burner.

[0022] A first embodiment of the burner 20 will be described in moredetail below with reference to FIGS. 2 and 3, wherein FIG. 2 is asectional view of the front portion of the burner and FIG. 3 is a frontview. This burner is adapted to be used with fuel in the form of a gas,such as propane, natural gas, or butane, or with oil fuel.

[0023] The burner 20 comprises a main portion 24, to which the supplylines 21-23 and 25 shown in FIG. 1 are connected. The portion 24 isprovided with an essentially circular cross-section, see FIG. 3, inwhich the configuration of the supply lines 21-23 appears in moredetail. Fuel is supplied through the first supply line 21 in the form ofsix equidistant pipes 21 a-f placed at a constant distance from thecentre axis of the main portion 24. Oxygen is supplied through anannular outer portion 22 and thus surrounds the fuel supplied throughthe pipes 21 a-f. Finally, sludge is supplied through the pipe 23, whichis co-axially placed in the burner.

[0024] In the pipe 23 for the sludge, there is provided an atomisingarrangement, designated 26. This functions in the following way. Theatomising medium, such as oxygen, is input to the burner at 25 through anumber of pipes. These pipes end in the central pipe 23 for the sludgeand connect thereto in an angle thereto, thereby atomising or dividingthe sludge leaving the pipe 23.

[0025] As already mentioned, the burner 20 is mounted in the side-wallof the furnace 30. In the preferred embodiment, the burner can betilted, i.e., can be positioned in different angles relative to thehorizontal and the vertical. The different orientations can be used forobtaining desired characteristics for the burning process.

[0026] In the following, the method for treatment of sludge will bedescribed in detail.

[0027] Initially, sludge is supplied to the container 42 of the feeder40. The sludge is of the above mentioned character, i.e., it has aliquid part and metal-containing particles intermixed in that liquidpart. The metal-containing particles comprise metal, metal oxide ormetal hydroxide.

[0028] The sludge is transferred from the container and into the feedingpump 45, wherein it is transported to the burner 20 by means of the pump45. The rate by which the sludge is fed to the burner is determined bythe speed of the feeding pump 45.

[0029] The operation of the oxy-fuel burner 20 is controlled by means ofthe amount of fuel and oxygen supplied through the first and secondsupply lines 21 and 22, respectively. The supply lines are connected tosources of fuel and oxygen (not shown), as is conventional. A source ofatomising medium is also connected to the burner through input 25.

[0030] The operation of the burner 20 will now be described in detailwith reference to FIGS. 2 and 3, showing a gas or oil burner. Sludge issupplied through the central feeding pipe 23 at a rate that iscontrolled by the feeding pump. Before reaching a flame 27 resultingfrom the oxy-fuel mixture and possibly fuel contained in the sludge, thesludge is atomised by means of the atomiser 26. In some cases, thecombustion can be maintained by energy contained in the sludge and inthose cases the fuel supplied through the supply line 21 is used mainlyfor starting the combustion. Thus, the sludge leaving the front portionof the burner is divided into small fractions, making an efficientheating thereof possible.

[0031] Fuel is supplied in the feeding pipes 21 a-f, see FIG. 3, whilean envelope of oxygen is supplied through the annular feeding area 22.The oxy-fuel mixture results in the flame 27 having properties, such aslength, temperature etc., that are controlled by the supply rate of fueland oxygen. The higher the oxygen content, the higher the temperature,resulting in a theoretical flame temperature of approx. 1500° C. ormore. Thus, the sludge is injected into the central portion of theflame.

[0032] As is seen from FIG. 2, the metal containing particles of thesludge injected into the flame is brought to agglomerate, thus creatingagglomerates of a larger size than the particles found in the sludge.The agglomeration process is controlled by means of several parameters,of which can be mentioned: temperature and velocity of the flame 27,energy content or density of the injected sludge, stoichiometry, i.e.,the ratio oxidising gas to added fuel, the oxygen content of theoxidising gas, the supply rate of oxygen and added fuel, the rate ofinjection of sludge and its characteristics, the travel time of thesludge in the flame, and burner characteristics and configuration, suchas tilting.

[0033] The wet part of the sludge is vaporised by the high temperatureof the flame, resulting in exhausts rising through the furnace 30 andsubsequently leaving through the exhaust outlet 34. The createdagglomerates and droplets fall to the bottom of the furnace 30, whereinthey are added to the charge 36. The charge is subsequently used inliquid or solid phase as it is. Alternatively the charge is returned toa process.

[0034] A preferred embodiment of the method and the apparatus accordingto the invention has been described. The person skilled in the artrealises that this can be varied within the scope of the appendedclaims. Thus, although an oxy-fuel burner 20 has been shown, otherconventional burners can be used, such as plasma burners or in somecases air-fuel burners having a high thermal efficiency.

[0035] Furthermore, a separate furnace unit 30 has been shown. Themethod according to the invention is equally applicable to other kindsof furnaces, such as electric arc furnaces, induction furnaces,reverberatory furnaces, electrically heated furnaces, blast furnaces,cupola furnaces, and converters etc.

[0036] Also, in the described embodiment, the burner is positioned in aside-wall of a furnace. However, it is realised that other suitablepositions are possible, such as in the upper part of the furnace. Also,a configuration with more than one burner is possible. It is thenpossible to inject the atomised sludge between three burner flames, forexample.

[0037] In the described embodiment, the sludge is fed to the furnace bymeans of a feeding pump. However, the sludge supplied to the furnacecould also be free-flowing etc.

[0038] A specific burner configuration has been shown. It is alsoappreciated that any suitable burner configuration having differentnumber of pipes etc can be used.

[0039] A separate input for atomising medium has been described. It isrealised that the same oxygen source can be used for both the atomisingmedium and the burner feed.

1. A method for treatment of sludge, said sludge having a liquid partand metal-containing particles intermixed therein, wherein saidparticles comprise metal, metal oxide or metal hydroxide, said methodcomprising the following steps: a) atomising said sludge; b) supplyingsaid atomised sludge to a flame of a burner provided in a furnace; c)bringing the liquid part of said sludge to vaporise by means of saidflame while maintaining said flame by means of a separate fuel supply;and d) bringing at least part of said metal-containing particles to meltby means of said flame.
 2. The method according to claim 1, comprisingthe additional step of: e) recovering said metal-containing particles inliquid or solid phase.
 3. The method according to claim 1 or 2, whereinsaid burner is an oxy-fuel burner.
 4. The method according to claim 1 or2, wherein said burner is a plasma burner.
 5. The method according toany of claims 1-4, wherein the metal content of said sludge is at least5% more preferably at least 20%, and most preferably at least 50%. 6.The method according to any of claims 1-5, wherein said sludge is awaste product from a process.
 7. The method according to any of claims1-6, wherein said flame is maintained mainly by energy contained in saidsludge.
 8. An apparatus for treatment of sludge, comprising: a container(42) for sludge having a liquid part and metal-containing particlesintermixed therein, wherein said particles comprise metal, metal oxideor metal hydroxide; a burner (20) having a flame (27) during operationthereof, said burner having a fuel supply line (21) for maintaining saidflame, a feeding pipe (23) for feeding sludge to said flame, and anatomiser (25, 26) for atomising said sludge; and a feeder (45, 46)connected between said container and said burner for supplying sludgefrom said container to said burner.